Known vibration proof structures of seat apparatuses (seats) for vehicles are disclosed, for example, in JP2011-235727A and JP2011-510863A (which will be hereinafter referred to as References 1 and 2). In particular, the vibration structure according to Reference 1 is an inner and outer double structure in which a lower end portion of a side frame of a seat back is configured so that an inner frame is arranged at an interior side of an outer frame. In addition, an elastic member is provided between the inner frame and the outer frame. Further, according to Reference 2, the seat includes sub-frames (side frames) of a seat back and a rod connecting the side frames to each other. Reference 2 discloses a structure in which an elastic member is provided between the rod and one of the side frames. In both References 1 and 2, an energy generated by a movement of a seat element (for example, the seat back, a seat cushion, and the like) supported to be arranged at an upper side of the seat is reduced by the elastic member arranged between components of the seat; thereby, vibrations generated at the seat may be reduced or absorbed.
As described above, according to the vibration structures of References 1 and 2, the elastic member is arranged between the components of the seat; therefore, rigidity of the seat may deteriorate. In particular, according to the vibration proof structure of Reference 2, the elastic member is provided between one end portion of the rod and the side frame; thereby, the deterioration of the rigidity of the seat is restricted. In fact, the seat requires the highest rigidity for a rear side thereof; however, in this point, the vibration proof structure disclosed in Reference 2 may not ensure the high rigidity for the rear side of the seat.
A need thus exists for a vibration proof structure of a seat apparatus for a vehicle, which is not susceptible to the drawback mentioned above.